FIG. 1 illustrates one example of a cellular communications network 10. In this particular example, the cellular communications network 10 is a Long Term Evolution (LTE) network. The cellular communications network 10 includes a Radio Access Network (RAN) that includes base stations 12-1 through 12-3, which for LTE are referred to as eNodeB's, that serve mobile terminals (not shown) located in corresponding cells 14-1 through 14-3. Mobile terminals are referred to herein as User Equipments (UEs). The base stations 12-1 thorough 12-3 are generally referred to herein collectively as base stations 12 and individually as base station 12. Likewise, the cells 14-1 through 14-3 are generally referred to herein collectively as cells 14 and individually as cell 14. Only three base stations 12-1 through 12-3 are illustrated in FIG. 1 for clarity and ease of discussion. However, the cellular communications network 10 typically includes many base stations 12 and corresponding cells 14. For LTE, each cell 14 includes one or more (e.g., 3) sectors.
The cellular communications network 10 further includes a core network 16 that includes Serving Gateways (S-GWs) 18-1 and 18-2, which are generally referred to herein collectively as S-GWs 18 or individually as S-GW 18, and Mobility Management Entities (MMEs) 20-1 and 20-2, which are generally referred to herein collectively as MMEs 20 and individually as MME 20. While two S-GWs 18 and two MMEs 20 are illustrated in this example, the core network 16 typically includes many S-GWs 18 and MMEs 20. In LTE, the base stations 12 are connected to the appropriate S-GWs 18 via S1-u connections and connected to the appropriate MMEs 20 via S1-c connections. Similarly, the base stations 12 are connected to one another via X2 connections. The S-GWs 18 are user plane nodes connecting the core network 16 to the RAN. Among other things, the S-GWs 18 serve as mobility anchors when UEs move between the cells 14 served by the base stations 12 as well as mobility anchors for other 3rd Generation Partnership Project (3GPP) technologies (Global System for Mobile Communications (GSM)/General Packet Radio Service (GPRS) and High Speed Packet Access (HSPA)). The MMEs 20 are control plane nodes of the core network 16. The responsibilities of the MMEs 20 include connection/release of bearers to UEs, handling of idle to active transitions, and handling of security keys.
One issue with the cellular communications network 10 of FIG. 1 is that localized capacity requirements may exceed the capabilities of the cellular communications network 10. For example, in a city, a large number of UEs may be located in particular areas within the cells 14 (e.g., a large number of users may be located along the streets of the city). Another issue with the cellular communications network 10 of FIG. 1 is that there may be localized coverage holes. For example, in a city, the base stations 12 are typically placed on top of buildings and coverage holes can occur at the street level and inside buildings.
Heterogeneous cellular communications networks have emerged to provide increased localized capacity (e.g., wireless hotspots) and increased coverage (e.g., address localized coverage holes). One example of a heterogeneous cellular communications network 22 is illustrated in FIG. 2. As illustrated, the heterogeneous cellular communications network 22 includes a RAN including a macro base station (BS) 24 serving a macro cell 26 and micro base stations 28-1 and 28-2 serving corresponding micro cells 30-1 and 30-2. The micro base stations 28-1 and 28-2 are generally referred to herein collectively as micro base stations 28 and individually as micro base station 28, and the micro cells 30-1 and 30-2 are generally referred to herein collectively as micro cells 30 and individually as micro cell 30. Note that while only one macro base station 24 and two micro base stations 28 are illustrated in this example, the heterogeneous cellular communications network 22 may include any number of macro base stations 24 and micro base stations 28. As one example, the heterogeneous cellular communications network 22 may be deployed in a city where the macro base station(s) 24 are located on the top of buildings and the micro base stations 28 are located at street level. The heterogeneous cellular communications network 22 also includes a core network 32 including a S-GW 34 and a MME 36.
One issue with heterogeneous cellular communications networks such as that shown in FIG. 2 is that UEs can quickly transition across many micro cells. For instance, multiple adjacent micro cells may provide coverage along busy streets. UEs, such as those of users inside moving automobiles, quickly transition across many micro cells. The quick transition of the UEs across many micro cells results in significant handover and paging overhead on the heterogeneous cellular communications network. As an example, FIG. 3 illustrates a heterogeneous cellular communications network 38 that includes micro base stations 40-1 through 40-3 (generally referred to herein collectively as micro base stations 40 and individually as micro base station 40) that serve three adjacent micro cells 42-1 through 42-3 (generally referred to herein as micro cells 42 and individually as micro cell 42). The micro base stations 40 may, for example, provide coverage along a busy street. A UE 44 quickly transitions across the micro cells 42. The quick transition of the UE 44 across the micro cells 42 results in multiple handovers (HO 1 and HO 2) in a relatively short amount of time.
In light of the discussion above, there is a need for systems and methods for reducing handover and paging overhead in heterogeneous cellular communications networks.